1. Field of the Invention
The present invention relates to a method of reforming a metal can end, and more particularly, to a method of reforming a circular can end having an annular groove around a center wall portion and a flange around the periphery of the can end which is typically seamed to a cylindrical can body containing beer or other carbonated beverage.
2. Description of the Prior Art
The prior art discloses numerous examples of metallic end closures for cans. The majority of such can ends have an end wall with an opening panel therein, an annular groove around the top end wall and a flange around the periphery of the can end.
The required gauge of the sheet metal end closure to be seamed onto a cylindrical beverage can body is determined by the yield and tensile strength required to resist buckling of the end closure at internal pressures of approximately 90 pounds per square inch. Typical end closures are able to tolerate internal pressures of approximately 85 to 90 pounds per square inch without significant distortion or buckling. Buckling is a phenomenon that primarily occurs when at least a portion of a chuckwall of a can end seamed onto a cylindrical can body is pulled upwardly and radially inwardly away from its connection to the can body in response to high internal pressures. Results of buckling may be exhibited as minor outwardly deformations in the generally planar can end and may range to a complete blow-out of the can end from the can body. The problems associated with buckling of a can end include premature opening of the can end or the easy open panel therein and vertical can stacking difficulties.
Prior art disclosures pertaining to reinforcement of can ends include U.S. Pat. No. 3,774,801 which relates to shaping or flexing the inner wall of a U-shaped reinforcing groove of a can end with radially separated concave areas of curvature to improve the can end's resistance to internal pressure. Of interest, also, is U.S. Pat. No. 3,843,014 which discloses a cover for a container with a peripheral neck having a radius of curvature within the range of 0.5 to 1.2 mm (approximately 0.020 to 0.047 inches) and a substantially rectilinear portion integral with and connecting the neck with a central portion. Such formation allegedly permits reduction in thickness of the can end on the order of 10 to 20 percent with internal pressure resistance capability equal to that of the conventional can end.
Another prior art disclosure of interest is U.S. Pat. No. 3,912,113 which pertains to an end panel for a container including a well having at its base a partial score and an opening flap. This patent discloses the provision of a coined area in the panel encompassing the well in order to inhibit distortion or blow-out of the opening flap in the end panel due to internal over pressurization.
Attempts at drawing, in a single step, a metal blank into a can end having a sharper than usual radius of curvature at the bottom of the annular groove have resulted in shearing or otherwise damaging of the sheet metal at or near the annular groove. The sheet metal blank is too thin to be drawn to such sharp radii of curvature in a single operation. Additional reforming steps to form reinforced can ends require an added investment in equipment, such as a press.
Accordingly, a new and improved method of producing a pressure resistant can end by reforming a conventional metallic can end is desired to increase the pressure holding capabilities of the container to which the can end is seamed.